What is CVE-2025-4144?

CVE-2025-4144 is a critical-severity vulnerability in Cloudflare Workers-Oauth-Provider, classified under Improper Authentication. CVSS score: 9.8/10. Published 2025-05-01.

How severe is CVE-2025-4144?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Auth bypass in Cloudflare Workers-Oauth-Provider

CVE-2025-4144

PKCE was implemented in the OAuth implementation in workers-oauth-provider that is part of MCP framework https://github.com/cloudflare/workers-mcp . However, it was found that an attacker could cause the check to be skipped. Fixed in: https://github.com/cloudflare/workers-oauth-provider/pull/27 https://github.com/cloudflare/workers-oauth-provider/pull/27 Impact: PKCE is a defense-in-depth mechanism against certain kinds of attacks and was an optional extension in OAuth 2.0 which became required in the OAuth 2.1 draft. (Note that the MCP specification requires OAuth 2.1.). This bug completely bypasses PKCE protection.

Vulnerability class: Broken Authentication

EPSS: 0.005 (41.5th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Cloudflare Workers-oauth-provider — versions 0.0.5

Weakness classification (CWE)

CWE-287 — Improper Authentication

References

cna@cloudflare.com (Patch, Issue Tracking)

Frequently asked questions

What is CVE-2025-4144?: CVE-2025-4144 is a critical-severity vulnerability in Cloudflare Workers-Oauth-Provider, classified under Improper Authentication. CVSS score: 9.8/10. Published 2025-05-01.
How severe is CVE-2025-4144?: Critical severity. CVSS v3 base score is 9.8 out of 10.